You can change the left side navigation very easily by adding the below attribute to the body tag in the views/partials/main.php
file.
data-layout="vertical"
data-sidebar-size="lg"
data-sidebar-size="md"
data-sidebar-size="sm"
data-content="fluid"
data-content="boxed"
data-skin="default"
data-skin="bordered"
data-sidebar="light"
data-sidebar="dark"
data-sidebar="brand"
data-sidebar="modern"
data-topbar="light"
data-topbar="dark"
data-topbar="brand"